Project Summary There are striking sex differences in stress/mood associated disorders such as anxiety and depression with women showing 2-3 fold greater prevalence than men. These differences are postulated to be regulated by sex- specific patterns of gonadal hormone exposure and their subsequent effect on brain circuitry, although little is known about these sexually dimorphic circuits. Recent studies in our laboratory have uncovered two cell groups which show sex differences in expression of corticotropin releasing hormone receptor 1 (CRFR1) in the paraventricular hypothalamus (PVH; males>females) and anteroventral/rostral periventricular hypothalamus (AVPV/PeN; females>males). In rodents, corticotropin releasing factor signaling (CRF) through CRFR1 is known to regulate anxiety and depressive-like behaviors as well as stress hormone (adrenocorticotropic hormone (ACTH), glucocorticoid)) secretion, although the specific function of these sexually dimorphic nuclei are currently unknown. Aim 1.1 will determine the role of PVH and AVPV/PeN CRFR1 populations in stress-associated behaviors and hormone responses by pharmacologically ablating CRFR1 cells in these regions. This will be accomplished by utilizing stereotaxic injections of toxin that specifically destroys CRFR1 cells. Anxiety/depressive-like behaviors and ACTH/glucocorticoid responses to psychological stress will be assessed in these mice. In Aim 1.2 we will determine the functional connectivity of these two cell groups with other stress-regulating brain sites. These studies will utilize cutting edge tract tracing tools to assess downstream projection sites of CRFR1 cells that are engaged during psychological stress. Altogether, this aim will reveal specific anatomical populations involved in sexually dimorphic regulation of behavioral and hormonal stress functions. Aim 2 will determine the role of estrogen receptor alpha (ER?)-containing CRFR1 neurons in regulation of stress- associated functions by generating and testing a conditional knockout mouse line. Our preliminary data indicate that a high percentage of CRFR1 cells in the PVH and AVPV/PeN co-localize ER?. Furthermore, ER? is known to regulate anxiety/depressive behaviors and stress hormone release. Therefore, ER? may be a key receptor through which gonadal hormones can affect stress-related functions. Mice with conditional deletion of ER? will be compared to control mice in rodent tests of anxiety, depression, and stress-induced hormone release. This aim will reveal a specific cell phenotype involved in gonadal hormone regulation of stress-associated functions.